The present invention comprises an improvement with respect to the basic crane structure shown in my U.S. Pat. No. 3,836,010 and applied to tower cranes in my U.S. Pat. Nos. 4,170,309 and 4,243,148. In these embodiments, a crane boom or supporting vertical tower is mounted on a pivotable load platform supported by a mobile transporter. A counterweight structure is independently supported on a second load platform pivotally carried by a second mobile transporter. The two platforms are interconnected by a rigid stinger that transmits rotational force about them during pivotal movement of the boom or tower. The platforms, transporters, and booms can be specially designed or can be constructed by using one or two conventional cranes as structural components in the compound configuration.
The cranes in question are utilized for lifting extremely high loads at substantial heights and over a substantial load radius. To make most effective use of the structural components of the crane, they are preferably longitudinally aligned in a straight row, with the upright elements in vertical positions. This aligns all of the structural components behind the load being lifted and eliminates bending forces on the structural components. The crane configurations feature high capacity lifting capability characteristic of fixed stiffleg or luffing derrick equipment, coupled with the mobility and flexibility of crawler cranes.
The structural size of such equipment exposes the cranes to the possibility of transverse wind loads which might topple with tower or boom while the crane is unattended. Since the heavy counterweight structure is remote from the load platform supporting the boom or tower, that load platform does not have the weight available which typically resists wind loading on conventional single platform crane structures. Furthermore, it is desirable that the two mobile platforms be independently pivotable about the stinger axis for ground mobility. The load platform supporting the boom or tower is therefore free to rotate about the stinger axis without any resistance from the counterweight platform.
Prior efforts to provide lateral stability to large upright booms have included the use of dual upright booms in an A-frame configuration which spreads the base below the boom. An example as shown in U.S. Pat. No. 3,868,022. Another approach is illustrated in U.S. Pat. No. 4,258,852 which uses an in-line boom and mast, and two horizontal stingers leading back to a pair of transversely spread counterweight trailers. This again is stated to provide additional lateral stability.